My Opinion On Powders High Humidity Performance


Apr 7, 2019
First this is just my opinion and could be completely wrong from the start.

Some powders are said to perform better in humid or wet conditions. I don’t share this perception, and allow me to explain why.

Once a cartridge is loaded it becomes a sealed environment. External conditions have no impact on burn rate or speed of the powder in the case. The atmospheric conditions inside the cartridge remain the same as they were when it was originally loaded.

The difference in atmospheric conditions eg, barometric pressure, and humidity impact performance of the bullet not the powder propelling it. Barometric pressure and humidity exert different influences upon the fired bullet, not the propelling charge. Heavier more humid air at sea level will exert different forces upon the bullet than light dry air at 10,000 feet above sea level. All the while, the conditions within the cartridge remain constant and identical to the conditions when the cartridge was loaded.

So I don’t think humidity and barometric changes have any impact on powder performance. I instead feel it impacts the fired bullet interacting with those different environmental conditions.

What do you gentleman think about this?


May 26, 2018
I don't see influence on the powder in the case either.
On bullet performance once it left the barrel: yes. On longer distances

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Feb 20, 2017
Honestly, I've never seen any discussion on humidity sensitive powders... This is a new one to me.

I guess if you lived on the coast in OR or BC where you are practically in a rainforest, than it could make some difference if the ammo was stored in an un-conditioned space... A noticiable difference in burn rate would be seen from a fresh can to an open and acclimatized can of powder; but the moisture content of loaded ammo stored in a conditioned space shouldn't change much...

Given that this is new to me, I'm guessing that some guys are drawing some wrong conclusions from the military's sealing of primers and bullets. In military ammo the bullets and primers are generally (supposed to be) sealed (WWI and WWII was with a lacquer or tar like substance) to keep moisture out. Moisture can be driven through those areas very slowly on a molecular level. This is particularly important in stupidly high humidity levels like the south pacific, rainforests, jungles, etc with extended periods of time like months. Hunters going after dangerous game in the Africa jungles will usually have sealed ammo - ... 67321.aspx.

I'll quote from ... ammunition as I think it may hold where the desire to have a moisture insensitive powder noted in the OP may come from.

"What does all this and my testing tell us? Well, if your ammunition — common consumer/sporting ammunition — gets submerged in water for a minute or less, don’t worry about it. However, after somewhere between 60 seconds and 24 hours of submersion, you can start to expect to potentially see deterioration in performance. But, aside from about a 10 percent failure rate, and possibly very slightly slower velocities, are there any other concerns?

There is. According to Gary Gronfor, one of the smart guys at Federal Ammunition, “Once ammunition has been wet, submerged or in a wet range bag or hunting coat, it becomes unreliable and untrustworthy. Moisture can enter thru the primer pocket, the crimp, the case mouth, or around the head on a shotshell, contaminating the primer and/or the propellant. The result is a bullet or wad in bore [a squib load where the bullet fails to fully exit the barrel] which undetected leads to bulged or blown barrels, other types of gun damage and possible injury to the shooter or bystander. Numerous times every year, we get ammunition and damaged guns and barrels that we are able to determine, that the ammo has been moisture contaminated."

Guy Miner

Master Loader
Apr 6, 2006
"Honestly, I've never seen any discussion on humidity sensitive powders... This is a new one to me."

Same here. Much discussion re humidity and flight of the bullet, but not on the performance of the powder.

Regards, Guy